If your friend is able to figure out her passphrase, it would be a good idea to add her passphrase to her backups.
Then she shouldn't included passphrase if the backup will be together because the 12-24 word seed phrase is enough to protect her coins if not revealed to anyone. The backup suppose not to be along with the seed phrase backup in my opinion.
I am not sure what path ledger uses by default
Ledger Nano uses the derivational path that you posted above (m/84'/0'/0'/0) for native segwit address generation.